Semi-conductor motor control system

Abstract

A semi-conductor system for controlling three phase motors by voltage and/or frequency variations. An input circuit provides dc power, such as a three phase full wave input bridge with silicon control rectifiers to provide a voltage controlled dc power output. An output inverter bridge having six silicon rectifiers receives dc power and converts it to three phase ac power for operating an induction motor. A diverter network is connected between the dc power input circuit and the output inverter and is activated periodically for temporarily diverting the dc power from the inverter in order that the inverter rectifiers may be turned off. The diverter may include a tank circuit having a capacitor and an inductor connected across the dc power output through a diode and a silicon control rectifier is connected to the tank circuit for shunting the dc power from the inverter and applying a reverse voltage to the inverter. A harmonic suppression circuit is connected across the output of the converter and may include a capacitor connected between each of the three phase output lines of the inverter.

What is claimed is: 
     
       1. An electrical circuit for varying the operation of a three phase electrical ac motor comprising, an input circuit for providing a dc current output,   an output inverter bridge having six silicon controlled rectifiers for receiving dc current and converting the dc current to three phase ac power for operating a three phase electrical motor,   a diverter network means connected between the input circuit and the output inverter activated periodically for temporarily diverting the dc current output from the inverter in order that six silicon controlled rectifiers may be turned off,   said diverter network includes, a tank circuit having a capacitor and inductor connected across the dc current output through a first diode,   an additional silicon controlled rectifier connected to said tank circuit for shunting off the dc current from the inverter and applying a reverse voltage to the inverter for turning off all of the silicon controlled rectifiers of the inverter, and   a second diode connected in parallel with the additional silicon controlled rectifier for providing a full cycle resonance of the tank circuit.     
     
     
       2. The apparatus of claim 1 including a harmonic suppression circuit including, a capacitor connected between each of the three phase outputs of the inverter.   
     
     
       3. An electrical circuit for varying the operation of a three phase electrical ac motor comprising, an input circuit for providing a dc current output,   an output inverter bridge having six silicon controlled rectifiers for receiving dc current and converting the dc current to three phase ac power for operating a three phase electrical motor,   a diverter network means connected between the input circuit and the output inverter activated periodically for temporarily diverting the dc current output from the inverter in order that six silicon controlled rectifiers may be turned off,   said diverter network includes, a capacitor and inductor connected in parallel across the dc current output through a first diode,   an additional silicon controlled rectifier connected in series with said inductor for shunting off the dc current from the inverter and applying a reverse voltage to the inverter for turning off all of the silicon controlled rectifiers of the inverter, and   a second diode connected in parallel with the additional silicon controlled rectifier for providing a full cycle resonance of the tank circuit.     
     
     
       4. The apparatus of claim 3 including a harmonic suppression circuit including, a capacitor connected between each of the three phase outputs of the inverter.